High-frequency wavemeter



Filed YJuly l0, 1947 ATTOR/VE V Patented Oct. 23,1951

HIGH-FREQUENCY WAVEMETER John E. Wolfe, Manhattan, Kans., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 10, 1947, Serial No. 760,020

3 Claims. 1

This invention relates to the art of signaling with ultra-high frequency electromagnetic waves and more particularly to wavemeters for determining the frequencies of such Waves.

In ultra-high frequency wavemeters, it is desirable to have as high a frequency range as possible consistent with precision and small size.

An object of this invention therefore is to provide a relatively small wavemeter of simple construction which will permit rapid and precise determination of the frequency of an ultra-high frequency wave which may be any one of the frequencies falling within a broad band of such frequencies.

The components of the preferred form of this invention described in detail hereinafter include a resonator comprising a calibrated, adjustable, tuned circuit, means for loosely coupling this circuit to the source of the ultra-high frequency wave of which the frequency is to be determined, and means for loosely coupling the tuned circuit to an external detector and indicating circuit associated therewith, the adjustable tuning means including a micrometric precision arrangement, with the tuned circuit comprising inductance and capacitance, the inductance beingl variable toward one end of the range of the resonator, and the inductance constant and the capacitance variable toward the other end of its range.

A feature is that the wavemeter acts as a resonator of quarter wave resonant coaxial line of variable length toward one end of its range and as a resonator of constant inductanceand variable capacitance toward the other end of its range.

Another feature is the micrometric type of adjustment of the inner conductor of the wavemeter and its cylindrical type capacitance which makes possible more precise tuning adjustment than has been possible heretofore.

Still another feature is the cylindrical type capacitance at one end of the travel of the inner conductor of the resonator tuning circuit which results in a very much greater frequency range than previously available. The range may be in the order of ten to one, for example, 1,500 megacycles to 150 megacycles, whereas wavemeters previously available have ranges in the order of about four to one, for example, 1,200

megacycles to 300 megacycles.

Heretofore, wavemeters of the resonator type which use adjustable capacitance in their tuning circuit have been of such design that the larger part of the tuning range is spanned by a very small movement of the movable member as their adjustable capacitance members are brought closer together to increase the capacitance as the range limit is approached. This results in a non-linear calibration curve and loss of accuracy as the range limit is approached. This objection is overcome in the invention disclosed herein because the cylindrical type capacitance provided spreads the capacitance linearly over a considerable movement of the center conductor of the tuning circuit which results in making the tuning less critical, readings more accurate, a larger amount of capacitance available and a consequent increase in the frequency range at the low frequency end of its range.

The nature of the invention together with other objects and features thereof will appear more fully in the following description of a specic embodiment, references' being made to the accompanying drawing in which:

The single gure of the drawing shows mainly in section the wavemeter in accordance with this invention.

The wavemeter |00 is mounted on a base I0 by suitable brackets 20 which are attached to a tubular outer conductor 30. The tuning circuit comprises outer cylindrical conductor or member 30, inner cylindrical conductor or member 40 and two end members 50, 60, which are attached to outer conductor 30 by screws 3l. The

means for loosely coupling the tuning circuit to the source of the waves to be measured comprises a coaxial line 10 which has its outer conductor 'H terminating flush with the inner surface of outer conductor 30, being inserted in a hole in the latter, and inner conductor 'l2 which enters the coaxial line 10 through insulating bushing 13 the end of which is connected to the inner surface of outer conductor 30, for example, by soldering it thereto. The means for loosely coupling the tuned circuit to a detector and indicating device comprises a coaxial line 15, which is a replica of coaxial line 10 and which has its outer conductor 'I6 terminating flush with the inner surface of outer conductor 30, being inserted in a hole in the latter. and in which inner conductor 11 enters through insulating bushing 18 and which terminates in a loop 19, the end of which is connected to outer conductor 30. Coaxial line 'l0 is placed diametrically opposite coaxial line 15 in outer conductor 30 and both are located in outer conductor 30 near the end member 50.

The inner conductor 40 is threaded throughand which terminates in a loop '14,`

out its length with 32 threads per inch. It threadedly engages the end member 50 which has a threaded bushing 5I fitted in its outer end which threadedly engages the conductor 4i). The bushing 5I is held against rotation upon the rotation of conductor 49 by two diametrically opposite screws 52, these screws being in turn fitted in radially disposed slots in the sleeve so as to permit the spring 5G to exert pressure on the bushing to cause a predetermined amount of friction on the thread of conductor 4E so as to hold it and the drum 8E secured thereto in each adjusted position.

The inner end of conductor 4i! has a metallic cylinder 4I attached to it, for example by threads 44. The projecting end 42 of cylinder 4I has a ring or spacer 43 of insulating material, for example, polystyrene, cemented to it around its exterior. End member Sii has a cylindrical cavity 6| which has an inner diameter such that the end ring 43 of cylinder 4| can enter it and it is positioned so that by turning conductor '4S the 'cylinder 4| will progress toward the end 62 of cylindrical cavity 6I, with substantially uniform clearance throughout its travel. Spacer 43 serves to keep cylinder 4i accurately spaced when in cavity 6|. The outer end of conductor 43 may have a thumb nut 45 rigidly attached to it by set screw 45.

A rotor scale or micrometer wheel Sli is rigidly attached to conductor 4i! by a set screw 8i. The

wheel 80 is marked on its outer cylindrical surface 82 with 100 equal divisions suitably engraved thereon parallel to its axis and with numerical indicator markings also engraved thereon at every tenth division, for example, 1G, 20, 30, etc. It has a circular mark 83 engraved around its circumference. Scale 9@ is mounted by brackets 9i with its vface in the same horizontal plane as the axis of conductor 48 and with its engraved edge 92 parallel to the axis of conductor 4t and adjacent to the outer circumference of rotor scale wheel Bil, so that when conductor 40 is rotated by means of thumb nut 46, mark 83 will move along the -engraved edge of the scale Sil. The edge g2 is engraved in inches divided into thirty seconds of an inch. The 32 threads per inch on conductor 40 lpermit wheel 80 to make one revolution for each thirty-second of an inch of longitudinal move- -mentof conductor 4B. Wheel 3@ having 100 divisions on its Vouter cylindrical surface permits accurate movement of conductor 4! by amounts as small as one one-hundredth of one thirtysecond of an inch or less.

In the operation of the wavemeter, considering the capacitance member 4| to extend initially to the end of the cavity 6i in the end member lili, the capacity of the circuit is a maximum and therefore the resonant frequency is at its minimum. Turning the thumb nut 46 withdraws the cylindrical capacity member 4l from the cavity thereby decreasing the capacitance of the circuit. The capacitance is between the surface of the cylinder 4i and the side surfaces of cavity 6i so that it is the area common to the two that controls the capacitance of the tuned circuit. While t-he capacitor member 4l is in the cavity 6D, the inductance of the tuned circuit is constant. The frequency is raised in this manner up to the point where the end 42 of the cylindrical member 4| has inst left the cavity El, A continuous increase cf frequency is provided following this instance by another effect which takes over at that point. After the member leaves the cavity `GI there is substantially no capacitance effect between the end 42 and the end member Gil. However, the inductance of the tuned circuit is then decreased by further withdrawing the rod thereby further increasing the resonant frequency of the wavemeter. This may be considered more easily not in terms of inductance but by considering the resonator as a quarter wave resonant coaxial line. At the moment the end 4i is in line with the surface of the end member 6&3, the distance between the two end members 50 and 69 is a one-quarter wave for the resonant coaxial line formed by the outer cylinder i and the inner conductor 40. By withdrawing the rod or conductor 4D, the coaxial line decreases in size, the distance measuring the quarter wavelength being from the face of the end member 56 to the end 42 of the cylindrical member 4i. As this distance decreases the resonant Wavelength decreases, thereby increasing the frequency of the resonant circuit. It, therefore, is apparent that starting at point 3 on the calibrated scale, at which point the resonant frequency is a minimum, and slowly progressing to point zero, at which point the resonant frequency is a maximum, a wide range of frequencies is provided in which the variations are substantially linear because of, first, the change in capacitance of the circuit and, second, the change in the wavelength of the coaxial line.

The embodiment of the invention described maybe used in conjunction with any of the wellknown detector and indicating circuits which can be electrically connected to conductor l'i. These circuits may include an amplifier. The wavemeter of the invention is calibrated by connecting several known ultra-high frequency `wave sources in succession to conductor 'i2 and adjusting the position of conductor it for each frequency by means of thumb nut 44 until the associated detector circuit indicates resonance within the wavemeter (resonator), then reading the location of mark 83 on scale 90, and plotting a curve on coordinate paper with frequency as ordinates and inches as abscissae.

Although the preferred form of the invention as shown is provided with cylindrical condenser members, another form of the invention may be provided with a conical condenser member on the inner conductor and with a conical cavity in end member 60 into which the conical condenser member can enter.

While the features of this invention have been disclosed with reference to a specinc embodiment only, it, of course, is understood that various modifications may be made in the details of construction without departing from the scope of this invention as defined in the appended claims.

What is claimed is:

l. A wavemeter comprising a calibrated adjustable sharply tuned resonant circuit, said circuit including a hollow cylindrical member, rod means extending into said cylindrical member at its one end defining a quarter wave resonant coaxial line of variable length therewith to vary the resonance of said circuit at the upper range of frequencies of said wavemeter, capacitance means associated with said rod means and the other end of said cylindrical member dening an end loading capacitance to vary the resonance of said circuit at the lower range of frequencies of said wavemeter, means for loosely coupling a source of electromagnet energy to said tuned circuit, means for loosely coupling said tuned circuit to an external detector and means external to said circuit for reciprocating said rod means.

2. A wavemeter comprising a calibrated adjustable sharply tuned resonant circuit, said circuit including a hollow cylindrical member, a iirst end member closing one end of said cylindrical member and supporting a rst vrcapacitance member, a second end member closing the other end of said hollow cylindrical member and having an aperture therethrough, a rod extending through said aperture, a second capacitance member mounted at the end of said rod, said capacitance members having complementary forms, means for loosely coupling a source of magnetic energy to said tuned circuit, means for loosely coupling said tuned circuit to an external detector and micrometer means external to said circuit for reciprocating said rod with said capacitance members in juxtaposition to vary the capacitance of said circuit or with said capacitance members not in juxtaposition to vary the length of the resonance circuit to vary the resonant frequency substantially linearly over the range of the wavemeter.

3. A wavemeter comprising a calibrated adjustable sharply tuned resonant circuit, said circuit including a hollow cylindrical member, a rst end member closing one end of said cylindrical member and having a cavity therein communieating with said hollow cylindrical member, a second end member closing the other end of said hollow cylindrical member and having an aperture therethrough, a rod extending through said aperture, a capacitance member mounted at the end of said rod, said capacitance member having the general form of the cavity Within' said iirst end ymember and tting therein but electrically separate therefrom, means for loosely coupling a source of electromagnetic energyfto said tuned circuit, means for loosely coupling said tuned cir- -cuit to an external detector, inicrometric means lexternal to said circuit for reciprocating said rod with said capacitance membr in `said hollow cylindrical member external tosaid cavity to vary the inductance of said circuit or with said capacitance member in said cavity to vary the capacitance of said circuit, and calibrated means associated with the other end oi.' said rod to determine the position of said capacitance member.

' JOHN E. WOLFE.

REFERENCES The following references areof record in the file of this patent: l

UNITED STATES 

